Seasonal variation of the physico-chemical parameters and their influence on the planktonic algae in the Raut River, Balti city, Republic of Moldova

Physico-chemical parameters play a major role in determining the density, diversity and occurrence of phytoplankton in a freshwater body. The current study evaluated the physico-chemical parameters and dominant algal phyla in the Răut river, the largest and most important watercourse that crosses the Bălți urban ecosystem, Republic of Moldova. Quarterly, during the year 2022, water and phytoplankton samples were collected from 4 sampling sites located on the river course, in different sectors of the city, taking into account the anthropogenic activities in the study area. The water samples were analyzed for 11 physico-chemical parameters, along with the identification of algae species, following standard methodology. The correlation between the planktonic algae and the physico-chemistry of the water was carried out using the Pearson correlation test. Spatial variability exists both in the number of algae species and in the values of the physico-chemical parameters, with clear differences between the sampling sites. In turn, the concentrations of physico-chemical parameters deviated from the natural background of water quality, especially at S2, S3, S4. The planktonic algae were represented by 68 species from 4 phyla: Cyanophyta, Chlorophyta, Bacillariophyta and Euglenophyta. The dominant complex was represented by Chlorophyta and Bacillariophyta (74%). Therefore, strong and moderate correlations between the quality parameters measured were recorded. Negative correlations dominate in the present study, therefore algal diversity is closely related to physical and chemical factors of water such as pH, mineralization, chemical oxygen demand, biochemical oxygen demand, total suspended solids, nitrate, total phosphorus.